The copying and redistribution of commercial imagery, audio and video productions has long been a cause of lost revenues to the creators/producers of such material. The advance of technology has not only expanded the means of legitimate distribution for audio and visual/video works, but has also made it easier to copy these materials for unauthorized purposes. In addition, there is a need to monitor, verify and track broadcasts and other distributions of this content.
Various methods have been developed to eliminate or limit both sophisticated and unsophisticated illegitimate distribution as well as to monitor distribution. Some of these methods rely on physical means. Others employ an auxiliary embedded signal to control, monitor and track usage of the content.
In accordance with preferred embodiments of the present invention, a multi-bit auxiliary message (sometimes termed a “digital watermark”) is robustly embedded directly into the audio signal. Hardware or software systems can then read this message and, for example, and control, monitor or track usage of the content.
Key practical issues are addressed whereby the perceptual impact of this added message can be adjusted—both overall and as a function of the underlying audio content. In addition, robustness to various forms of distortion are addressed in a manner superior to the prior art.